This invention relates to railcar trucks and more particularly to friction shoes having a tapered vertical wall.
A typical freight railcar truck comprises wheelsets mounted on two axles which support side frames at each side of the railcar and a transverse bolster extending between the side frames with the ends thereof supported between two vertical columns on load springs carried by each side frame. Usually a truck is located under each end of a railcar and the car itself is pivotally supported upon a centerplate centrally positioned on each bolster. Thus the weight of the railcar will cause the ends of the bolsters to move vertically on the load springs while confined between the vertical columns.
To provide proper damping for the suspension system, friction shoes are spring biased in pockets to frictionally retard vertical movement between the bolster and the side frame columns. Although it is possible to locate such pockets in the side frame columns, it is more common to locate the pockets in the bolster, usually two opposed pockets at each bolster end. The friction shoes have vertically disposed walls with substantially flat, outward friction faces which contact friction plates secured to the opposite truck component. In certain types of such friction shoes there is a shoe slope surface, generally opposite the friction face, which declines from a top portion of the friction shoe to a bottom portion thereof and away from the friction face and which slope surface engages a sloped surface on the inside of the pocket. The latter type shoe also has a bottom opening or hole through which a control spring extends to the top portion of the shoe. Some friction shoes include elastomer pads or coatings on the sloped surfaces to reduce wear on those surfaces and thereby extend service life. The control spring urges the friction shoe against the pocket sloped surface and upwardly through the pocket, while the slope also guides the shoe outwardly of the pocket against the opposite truck member such as the friction plate on the frame vertical column.
The frictional forces of the friction shoe surfaces against both the sloped surfaces of the bolster end and particularly against the side frame column friction plates tend to damp the oscillations of the bolster relative to the side frame and thereby lessen the dynamic motions of the freight car.